Temperature management devices, such as heaters and air conditioners are used in many areas of modern life. One example of an area where temperature management devices are extensively used is the area of injection molding. Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
Within a typical molding system, a number of temperature management devices are used. For example, a barrel of an injection unit can be associated with one or more heaters for maintaining a desired temperature for plasticizing resin pellets (or other type of raw material) into melt having consistency suitable for injection into a molding cavity. A melt distribution network, also referred to sometimes as a “hot runner”, also utilizes one or more heaters to maintain the melt within the melt distribution network at the desired temperature during distribution of the melt between the injection unit and a given molding cavity of a multi-cavity mold.
In some implementations, an air conditioner and/or a dehumidifier can be used for maintaining a desired ambient temperature, for example, to prevent condensation occurring within the molding machine, when the molding machine is operated in certain regions of the world where the ambient humidity makes operation of the injection molding system susceptible to condensation.
The temperature management devices used within molding machines can be broadly divided into two categories: a multi-zone temperature management device and a single-zone temperature management device. Taking an example of a barrel heater for the injection unit, the barrel heater can have multiple control zones in the sense that a temperature setting of each control zone can be set and controlled independently of the temperature setting in other control zones. On the other hand, the barrel heater can be of a single-zone control type. Within this scenario, a single setting can be associated with the whole barrel heater disposed along the whole or part of the barrel.
Irrespective of the type of the temperature management device, inability to accurately control the temperature settings of the temperature management device can have undesirable consequences. Again, taking the example of the barrel heater, inability to precisely control the temperature setting can have multiple undesirable effects. For example, if the barrel heater maintains a temperature that is below the desired temperature, the resin will not reach the required molten state and will result in parts of undesired quality or in failure of the molding machine altogether. On the other hand, if the barrel heater maintains temperature which is above the required temperature, the resin can degrade which can leave undesirable marks on the parts (i.e. blemishes) or render the resin batch unusable altogether.
U.S. Pat. No. 5,173,224 issued to Nakamura et al. on Dec. 22, 1992 discloses a fuzzy inference thermocontrol method for an injection molding machine with a Proportional-Integral-Differential (PID) control. The disclosed system allows to perform automatic PID control corresponding a status of an injection molding machine for eliminating a temperature overshoot or an undershoot during thermocontrol of thermocontrolled components of the injection molding machine, the Fuzzy Control theory is used for controlling the injection molding machine. By using the Fuzzy Control system, the object temperature of the thermocontrolled components can be attained with practically eliminated overshoot and undershoot.
U.S. Pat. No. 5,043,862 issued to Takahashi et al. on Aug. 27, 1991 discloses a PID control method and PID controller for determining, from a control response from a process, characteristic values representative of controllability and automatically deriving and setting PID constants from the determined characteristic values. The error between a set point and a controlled value is decided as to whether to be due to a change in set point or due to a disturbance, and PID constants are set on the basis of results of decision.
U.S. Pat. No. 5,551,857 issued to Fujioka et al. on Sep. 3, 1996 discloses a cylinder temperature controller for an injection molding machine in which an injection molding operation is performed while keeping the injection cylinder at a stable preset temperature regardless of disturbances such as the change of mold temperature or ambient temperature and the temperature rise caused by the shear compression of resin. A temperature regulator for carrying out PID feedback control of the injection cylinder temperature is provided with a PID adjusting means unit for automatic tuning. The actual temperature T of each portion of the injection cylinder is detected by a thermocouple. When the actual temperature T deviates from a predetermined temperature range defined by an upper limit [A+B] and lower limit [A−B] which are set on the basis of the preset target temperature A, an automatic tuning command is outputted to the temperature regulator. Upon receipt of this command, the PID adjusting unit sets the PID parameters again at a value suitable to the disturbance. By keeping the PID parameters to be suitable to the disturbance, the actual temperature T of each portion of the cylinder agrees with the preset target temperature A regardless of the change of the disturbance.
U.S. Pat. No. 5,997,778 issued to Bulgrin on Dec. 7, 1999 discloses an injection molding machine uses a summed, multi-term control law to control ram velocity during the injection stroke of a molding cycle to emulate a user set velocity profile. An automatic calibration method sets no load ram speeds to duplicate user set ram speeds. Finite impulse response filters produce open loop, no load control signals at advanced positions on the velocity profile to account for lag in system response. An adaptive, error term indicative of load disturbance, observed from a preceding cycle is added at the advanced travel position predicted by the finite impulse response filter to produce a predictive open loop, load compensated control signal. Finally, an auto tuned PID controller develops a real time, feedback load disturbance signal summed with the open loop control signal to produce a drive signal for the machine's proportioning valve.